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POPULAR SCIENCE REVIEW. 
fusions .* In short, he has opened up a new and exact method, 
which must lead to a scientific determination of the existence 
and nature of the bacteria-germs. His beautiful experiments 
on the decomposition of vapours, and the formation of actinic 
clouds by light, led him to experiment on the floating matter 
of the air, and with what results is widely known. Confined 
and undisturbed air, however heavily charged with motes, 
becomes at length, by their deposition, absolutely clear, so 
that the path of the electric beam is invisible across it. From 
this, and associated indications, he acutely inferred “ that the 
power of developing life by the air, and its power of scattering 
light, would be found to go hand in hand ; ” so that a beam 
of light sent across the air into which infusions might be 
placed and examined by the eye, rendered sensitive by dark- 
ness, might be utilised with the best results in determining the 
existence of bacteria-germs. To bring the idea to a practical 
result a number of chambers were constructed with glass fronts. 
At two opposite sides facing each other a couple of panes of 
glass were placed to serve as windows, through which the 
electric beam might pass. A small door was placed behind, 
and an ingenious device was arranged to enable a germ-tight 
pipette to have free lateral, as well as vertical, motion. Con- 
nection with the outer air w 7 as preserved by means of two 
narrow tubes inserted air-tight into the top of the chamber. 
The tubes were bent several times up and down, “*so as to 
intercept and retain the particles carried by such feeble 
currents as changes of temperature might cause to set in 
between the outer and the inner air.” 
Into the bottom of the boxes were fitted air-tight large test- 
tubes, intended to contain the liquid to be exposed to the 
action of the moteiess air, 
“ On September 10 the first case of this kind -was closed. The 
passage of a concentrated beam across it showed the air within 
it to be laden with floatiug matter. On the 13th it was again 
examined. Before the beam entered, and after it quitted the 
case, its track was vivid in the air, but within the case it 
vanished. Three days quite sufficed to cause all the floating 
matter to be deposited on the sides and bottom, where it was 
retained by a coating of glycerine, with which the interior sur- 
face of the case had been purposely varnished. The test-tubes 
were then filled through the pipette, boiled for five minutes in 
a bath of brine or oil, and abandoned to the action of the mote- 
less air.” 
In this way the air in its normal condition Tvas freely supplied 
to the infusions, but of mechanically suspended matter it could 
“Nature,” Jan. 27, 1876, p. 252; and Feb. 3, p. 268. 
